The Unit of Molecular Signal Transduction directed by Tamas Balla investigates signal transduction pathways, that mediate the actions of hormones and growth factors in mammalian cells with special emphasis on the role of phosphoinositide-derived messengers. Current studies are aimed at (1) understanding the function and regulation of two novel phosphatidylinositol (PI) 4-kinases that control the synthesis of hormone-sensitive phosphoinositide pools; (2) characterizing the structural features that determine the catalytic specificity of PI 3- and PI 4-kinases; (3) defining the molecular basis of protein-phosphoinositide interactions via the pleckstrin homology domains of selected regulatory proteins; (4) determining the importance of these interactions in the activation of cellular responses by G protein-coupled receptors and receptor tyrosine kinases.